I have never done this. So i am just going to lend my thoughts. Grayceworks has some very good ideas. But being that i have used solid wood molds, i know how over time they can warp due to the heat of the soap. Formica is a series of layers of composite woods that are glued together, which i would think would make it more susceptible to warping. I would still try it though, and most definitely line it, when i drip my traced soap on my formica counters, and i don't clean it right away, it sticks like the dickens. Good luck!!!